1. Field of the Invention
The invention relates to a method of controlling radio links in a UMTS (Universal Mobile Telecommunications System) cellular system, and more particularly to a method for intelligent mobile assisted soft handover in a UMTS cellular system.
2. Description of the Related Art
The UMTS (Universal Mobile Telecommunications System) is a third-generation mobile communications system (3G) which provides an enhanced range of multimedia services. The mobile communication system can be divided into two segments: a radio access network (RAN) that performs air-interface related functions and a core network (CN) that performs switching functions and interfaces to external networks such as the internet or a public-switched telephone network. The third-generation mobile communication system provides improvements in both the radio access network RAN and the core network CN. Currently, the most common form of UMTS uses WCDMA (Wideband Code Division Multiple Access) as the underlying air interface and is standardized by the 3rd Generation Partnership Project (3GPP).
In mobile communications systems, while a mobile station (MS, also known as user equipment, UE) moves between different cells, a connection must be kept from being dropped by the network. Such a procedure is called “handover” or “handoff”. In CDMA or WCDMA systems, handover can be a hard handover or a soft handover. A hard handover is the process in which the MS is handed from one cell to the next in order to maintain a radio connection with the network. A hard handover results in the radio connection being broken between the network and the mobile, before a new radio connection is established with the network in the target cell. Meanwhile, a soft handover is the process where the radio links are added and abandoned in such a manner that the mobile always keeps at least one radio link established.